Fix clippy lints (#299)

* Fix clippy lints

- Replace MetricsError::NonExhaustive with #[non_exhaustive]
- Remove some redundant let bindings
- Disconnect rayon::scope from result handling

* Update proc-macro2 to fix compilation on nightly

av_metrics/src/lib.rs

@@ -19,6 +19,7 @@ pub mod video;
 ///
 /// This enum may be added to in the future and should not be assumed to be exhaustive.
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum MetricsError {
     /// Indicates an input file could not be read for some reason.
     #[error("Could not read input file: {reason}")]
@@ -56,8 +57,4 @@ pub enum MetricsError {
         #[doc(hidden)]
         reason: String,
     },
-    /// Placeholder
-    #[doc(hidden)]
-    #[error("Unreachable")]
-    NonExhaustive,
 }

av_metrics/src/video/mod.rs

@@ -159,7 +159,7 @@ trait VideoMetric: Send + Sync {
         let (send, recv) = crossbeam::channel::bounded(num_threads);
         let vid_info = decoder1.get_video_details();
 
-        match crossbeam::scope(|s| {
+        let scope_result = crossbeam::scope(|s| {
             let send_result = s.spawn(move |_| {
                 let mut decoded = 0;
                 while frame_limit.map(|limit| limit > decoded).unwrap_or(true) {
@@ -224,7 +224,9 @@ trait VideoMetric: Send + Sync {
                     .unwrap_or_else(|_| Err("Failed joining the sender thread".to_owned())),
                 process_error,
             )
-        }) {
+        });
+
+        match scope_result {
             Ok((send_error, process_error)) => {
                 if let Err(error) = send_error {
                     return Err(MetricsError::SendError { reason: error }.into());

av_metrics/src/video/psnr.rs

@@ -97,7 +97,6 @@ impl VideoMetric for Psnr {
 
         frame1.can_compare(frame2)?;
 
-        let bit_depth = bit_depth;
         let mut y = Default::default();
         let mut u = Default::default();
         let mut v = Default::default();

av_metrics/src/video/psnr_hvs.rs

@@ -85,7 +85,6 @@ impl VideoMetric for PsnrHvs {
 
         frame1.can_compare(frame2)?;
 
-        let bit_depth = bit_depth;
         let mut y = 0.0;
         let mut u = 0.0;
         let mut v = 0.0;

av_metrics/src/video/ssim.rs

@@ -246,7 +246,6 @@ impl VideoMetric for MsSsim {
 
         frame1.can_compare(frame2)?;
 
-        let bit_depth = bit_depth;
         let mut y = 0.0;
         let mut u = 0.0;
         let mut v = 0.0;